At a typical refueling station, fuel (such as gasoline, diesel, biofuels, blended fuels, or the like) is pumped from an underground storage tank through a fuel dispenser, a hose and associated nozzle to the vehicle fuel tank. As the fuel enters the vehicle fuel tank, hydrocarbon vapors from the fuel inside the tank are exhausted or forced out of the tank. Environmental laws and/or regulations require that vapors emitted from a vehicle fuel tank during refueling be captured and returned to the underground fuel storage tank. For example, stage II vacuum assist vapor recovery systems (i.e. vapor recovery systems utilized during vehicle refueling) may be required to capture/recover a certain percentage (such as 95%) of the fuel vapor that is exhausted from the vehicle tank during refueling. The captured vapor is returned through the vapor path of the nozzle, hose, dispenser and underground piping system back to the ullage space of the underground fuel storage tank.
An ever-increasing number of vehicles include an onboard refueling vapor recovery (“ORVR”) system configured to capture/reclaim the vapor emitted from the fuel tank during refueling. The ORVR system routes or feeds the vapor to a capture canister which includes activated carbon. Once the refueling process is complete and the vehicle engine is running, vapor in the capture canister is routed into the engine where the vapors are burned during the combustion process. The ORVR system is also vented so that the pressure in the vehicle fuel tank is maintained at or near atmospheric pressure.
A liquid seal ORVR system (the most common ORVR system) is typically designed such that the vehicle fill pipe leading to the vehicle fuel tank has a progressively reduced inner diameter. This configuration ensures that fuel flowing into the fill pipe covers or extends continuously across the cross section of the fill pipe during refueling to form a liquid seal, which prevents fuel vapor from escaping through the fill pipe. The reduction in diameter of the fill pipe also causes a vacuum to be generated during refueling due to the venturi effect. The phenomemon, known as an injector effect, draws surrounding air/vapor into the fuel flow stream, and creates a positive pressure in the vehicle fuel tank that forces the vapors into the vapor capture canister carried on the vehicle.
When a vehicle equipped with an ORVR system (i.e. an ORVR vehicle) is refueled by a dispenser with a vacuum assist vapor recovery system, the ORVR system collects the vapor from the vehicle fuel tank, thereby preventing the vapor from being collected by the vapor recovery system. Accordingly, since the vapor recovery system of the refueling station may continue to operate, the vapor recovery system could, instead of vapor, draw in fresh air surrounding the vehicle/nozzle interface and route the ingested fresh air to the ullage space of the underground storage tank. The introduction of excessive fresh air into the underground storage tank increases the evaporation of the liquid fuel stored in the underground storage tank. This increase in vapor, or vapor growth, in the underground storage tank causes the tank to become pressurized so that polluting fuel vapors escape the tank and are released into the atmosphere. Accordingly, the incompatibility between an ORVR system and a vacuum assist vapor recovery system can increase the hydrocarbon pollutants and reduce the overall effectiveness of each system.
Some vacuum assist vapor recovery nozzles may use a vapor boot or bellows which surrounds the end of the nozzle spout and contacts the fill pipe/body of the vehicle to contain vapors. In addition, many nozzles may utilize a shutoff sensor/opening positioned at or near the end of the nozzle spout. When the shutoff sensor is covered by foam or splash-back of the liquid fuel, the shutoff sensor triggers an automatic shutoff of the nozzle. Refueling systems that utilize a vapor boot and a shutoff sensor can experience nuisance or premature automatic shutoffs due to the vacuum generated by the liquid seal ORVR system. In particular, the vacuum created by an ORVR vehicle during refueling can trigger the shutoff sensor of the nozzle before the fuel tank is full. This requires the customer/operator to re-engage the nozzle, thereby adding wear and tear on the refueling components, and causing aggravation to the customer/operator.
Standard or non-ORVR vehicles (i.e. vehicles lacking an ORVR system) can also experience a temporary vacuum in the vehicle tank fill pipe in a condition known as “vapor collapse.” In particular, when the ullage space in the vehicle fuel tank is at a sufficiently elevated temperature and/or pressure, the vehicle may be considered to be a “hot” vehicle. When fuel from the underground storage tank is dispensed into the tank of a hot vehicle, the vapor in the hot vehicle tank is rapidly chilled by the cooler fuel, thereby correspondingly reducing the pressure in the ullage space of the vehicle fuel tank. As the vapor in the vehicle tank shrinks, a negative pressure or vacuum is created in the vehicle tank ullage space and fill pipe, resulting in vapor collapse.
Vapor collapse is typically a relatively brief event, and the reduced pressure caused by vapor collapse quickly dissipates as equilibrium is reached. However, many refueling systems include an ORVR sensor that can be activated by the temporary vacuum sensed in the fill pipe of the vehicle during vapor collapse. This, in turn, may cause the refueling system to block the recovery of vapor for the remainder of the refueling event. The failure to recover vapors during refueling allows the polluting vapors to escape into the atmosphere, and cause the refueling event to be non-compliant.
Moreover, when a refueling system incorrectly determines that a non-ORVR vehicle is an ORVR vehicle due to vapor collapse, the improper determination can cause the nozzle automatic shutoff mechanism to function improperly. In particular, in this case the refueling system blocks the vapor return path to the underground storage tank ullage space. When the vapor boot on the nozzle does not allow the vehicle ullage space to vent, pressure in the vehicle ullage space and vapor boot builds as fuel is dispensed and the vapor is trapped in the tank. The pressure could build to a point where the nozzle automatic shutoff mechanism will not function, which could cause the tank to overfill and fuel to spill on the ground.